全文获取类型
收费全文 | 2273篇 |
免费 | 296篇 |
出版年
2021年 | 19篇 |
2019年 | 12篇 |
2018年 | 29篇 |
2017年 | 15篇 |
2016年 | 29篇 |
2015年 | 60篇 |
2014年 | 66篇 |
2013年 | 96篇 |
2012年 | 117篇 |
2011年 | 127篇 |
2010年 | 76篇 |
2009年 | 67篇 |
2008年 | 127篇 |
2007年 | 103篇 |
2006年 | 79篇 |
2005年 | 78篇 |
2004年 | 80篇 |
2003年 | 77篇 |
2002年 | 65篇 |
2001年 | 64篇 |
2000年 | 74篇 |
1999年 | 61篇 |
1998年 | 30篇 |
1997年 | 22篇 |
1996年 | 32篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 46篇 |
1991年 | 47篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 52篇 |
1987年 | 55篇 |
1986年 | 38篇 |
1985年 | 44篇 |
1984年 | 45篇 |
1983年 | 32篇 |
1982年 | 26篇 |
1981年 | 31篇 |
1980年 | 17篇 |
1979年 | 50篇 |
1978年 | 28篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 17篇 |
1973年 | 25篇 |
1972年 | 18篇 |
1971年 | 20篇 |
排序方式: 共有2569条查询结果,搜索用时 15 毫秒
1.
2.
Summary PEG has been activated using epoxy-oxirane, epichlorohydrin and periodate based reactions. The coupling to activated PEG of several protein ligands of different sizes was investigated. Glutathione, trypsin inhibitor, Protein A and anti-BSA have been bound to PEG and used to increase the selectivity of protein separation in aqueous two-phase systems. 相似文献
3.
4.
Relationships between the strongyloid nematodesRugopharynx delta, R. zeta, R. omega, R. longibursaris, R. mawsonae andR. sigma, all from macropodid marsupials, were investigated using allozyme data. The phylogenetic trees derived from the electrophoretic data set were congruent with those of the hosts and were consistent with the hypothesis that the species complex originated in pademelons of the genusThylogale and diversified in rock-wallabies (Petrogale spp.) and scrub wallabies of the subgenusNotamacropus. Host switching is evident only between closely related macropodid taxa. 相似文献
5.
6.
The purpose of this study was to determine the impact of infant restraint on dyadic interactions and maternal foraging patterns. Five bonnet macaque (Macaca radiata) mother-infant dyads were observed under three conditions: high foraging demand for the mothers with nonrestrained contact between mothers and infants (HFD-NRC), high foraging demand with restrained contact (HFD-RC), and low foraging demand with restrained contact (LFD-RC). In the restrained contact conditions the infants lived in a nursery within the group pen that allowed dyadic nursing, contact, proximity, and grooming, but prevented the infants from being with their mothers in the remaining portions of the pen, including the foraging area. Observations began when the infants were a mean of 5.4 months old. HFD-RC resulted in decreased dyadic contact relative to HFD-NRC, but did not significantly affect foraging task engagement; there were, however, marked individual differences in the response patterns of the mothers. Dyadic contact was also decreased during the LFD-RC condition, but maternal patterns under low demand resulted in lower levels of infant contact initiation. This study demonstrated the feasibility of a nursery-restrained rearing paradigm in exploring the strategic patterns of coping with conflicting environmental and maternal demands in bonnet macaque mothers. © 1993 Wiley-Liss, Inc. 相似文献
7.
Kent M. Daane Monica L. Cooper Serguei V. Triapitsyn John W. Andrews Jr Renato Ripa 《Biocontrol Science and Technology》2008,18(1):43-57
To improve natural suppression of the obscure mealybug, Pseudococcus viburni (Signoret), the parasitoids Pseudaphycus flavidulus (Brèthes) and Leptomastix epona (Walker) (Hymenoptera: Encyrtidae) of Chilean origin were released in California's Central Coast vineyards from 1997 to 1999. A survey for parasitoids of P. viburni was conducted in the Edna Valley appellation wine grape region from 2005 to 2007, 6–8 years after classical biological control releases were discontinued. Two survey methods were used. First, field collections of obscure mealybugs from commercial vineyard blocks (2005–2007) and, second, placement of “sentinel mealybugs” on potted (1 L) grape vines (2006 only). From both survey methods, P. flavidulus was recovered, albeit levels of parasitism were low (less than 0.6%). We also placed longtailed mealybug, Pseudococcus longispinus (Targioni Tozzetti), on potted plants concurrent with placement of sentinel obscure mealybugs in the vineyard in order to measure parasitoid activity on this closely-related mealybug species. No P. flavidulus were recovered from P. longispinus. Other encyrtid parasitoids reared from either P. viburni or P. longispinus were Anagyrus pseudococci (Girault), Leptomastix dactylopii Howard, Leptomastidea abnormis (Girault), Coccidoxenoides perminutus Girault, and Tetracnemoidea peregrina (Compere). A hyperparasitoid, Chaetocerus sp., was also reared. The data are discussed with respect to biological control of vineyard mealybugs and newly developed controls for the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Because Pseudaphycus species reared from mealybugs are superficially very similar a taxonomic key and discussion of host relationships for selected Pseudaphycus species are provided. 相似文献
8.
Mark Andrews Alan Brown Jean-Yves Chiva David Fradet David Gordon Mark Lansdell Malcolm MacKenny 《Bioorganic & medicinal chemistry letters》2009,19(8):2329-2332
The reported selective serotonin Re-uptake Inhibitor Litoxetine was used as the starting point in the design of a range of potential SSRIs with high ease of synthetic accessibility. Preparation and subsequent optimization yielded a range of potent and highly selective SSRIs. 相似文献
9.
10.